Special Seminars on Numerical Modelling for Computational Fluid Dynamics have been presented recently at this Institute by Prof Dr Leopold Škerget, Prof Dr Matjaz Hriberšek and Prof Dr Niko Samec from the University of Maribor, Slovenia.
Prof Škerget gave the first presentation entitled ‘Numerical modelling of compressible natural convection by BEM’. Prof Škerget stated ‘most of the studies dealing with transport phenomena are based on presuming the fluid is incompressible and viscous, where the mass density is a constant quantity, and the velocity does not depend on the mass density.’ He then went on to say that ‘pressure in the incompressible fluid flow model is not a thermodynamic state variable, but simply a force in the linear momentum balance equation.’ Such an easy rheological model for the fluid is suitable for modelling of slow flows, or flows with small pressure and temperature gradients or no chemical reaction and therefore the mass density differences may be neglected. The presentation of the numerical algorithm based on the Boundary Element Method for computation of flows of real compressible viscous fluid was described, with restriction to subsonic flows.
The second presentation was given by Prof Hriberšek entitled ‘Numerical modelling of conjugate transport phenomena by BEM’ which dealt with an overview and computational aspects of Boundary Element and Boundary-Domain Integral Methods for computation of conjugate transport phenomena. It was made clear that governing equations consist of conservation of mass, momentum, heat energy and species. Prof Hriberšek went on to say that the continuum, for which these equations are to be solved, could be fluid, solid or porous media. His numerical algorithm uses the velocity-vorticity formulation and is based on vector-potential formulation of flow kinematics. The results are an accurate determination of the boundary vorticity values, allowing computations of flows in complex geometrics. In order to lower computational costs, the domain velocity computations are performed by the segmentation technique, and resulting linear systems of equations are solved by preconditioned Krylov subspace methods. In case of heat and mass transfer in solids, boundary only discretization or dual-reciprocity based domain discretisation can be used. The versatility of the developed numerical algorithm was tested on several benchmark and conjugate problems.
Prof Samec presented the final seminar entitled ‘Laboratory simulation of combustion in an incinerator starved of air’. CFD is used for reacting flows and the governing equations for turbulent reacting flows consist of mass, momentum, energy and mass species conservation equations. The influence of chemical reactions is involved in the source terms of the energy and mass species conservation equation applying the corresponding turbulent combustion model. There are many turbulent combustion models available for different combustion cases. Therefore it is necessary to find the most appropriate model for the specific case. Prof Samec has found that the Eddy Dissipation Combustion Model - EDCM seems to be the most appropriate for simulating combustion in the secondary chamber of pilot scale starved incinerator where gaseous combustion occurs after the gasification of solid waste in the primary chamber. Some combustion conditions (temperature, turbulence and time) were investigated and controlled applying EDCM and in cases of incomplete combustion some chemical kinetics effects should be included.